1. Field of the Invention
This invention relates to a light beam scanning apparatus, which is used in an image read-out apparatus, a laser printer, or the like for scanning a material is with a light spot.
2. Description of the Prior Art
Image recording and reproducing systems have heretofore been used in various fields. With image recording and reproducing systems, a recording medium, on which an image has been recorded, is scanned with a light beam, and an image signal is thereby detected from the recording medium. Appropriate image processing is carried out on the image signal. A light beam is then modulated in accordance with an image signal which has been obtained from the image processing. A recording medium, which is sensitive to the modulated light beam, is scanned with the modulated light beam, and a visible image is thereby reproduced on the recording medium.
For example, as disclosed in Japanese Patent Publication No. 61(1986)-5193, an X-ray image is recorded on an X-ray film having a small gamma value chosen according to the type of image processing to be carried out, the X-ray image is read out from the X-ray film and converted into an electric signal (image signal), and the image signal is processed and then used for reproducing the X-ray image as a visible image on photographic film or the like. In this manner, a visible image having good image quality with high contrast, high sharpness, high graininess, or the like, can be reproduced.
Also, when certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a sheet provided with layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to radiation which has passed through an object, such as the human body A radiation image of the object is thereby stored on the stimulable phosphor sheet. The stimulable phosphor sheet is then scanned with stimulating rays, such as a laser beam, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a recording material such as photographic film, on a display device such as a cathode ray tube (CRT) display device, or the like.
Radiation image recording and reproducing systems which use stimulable phosphor sheets are advantageous over conventional radiography using silver halide photographic materials, in that images can be recorded even when the energy intensity of the radiation to which the stimulable phosphor sheet is exposed varies over a wide range. More specifically, since the amount of light which the stimulable phosphor sheet emits when being stimulated varies over a wide range and is proportional to the amount of energy stored thereon during its exposure to the radiation, it is possible to obtain an image having a desirable density regardless of the energy intensity of the radiation to which the stimulable phosphor sheet was exposed. In order to obtain the desired image density, an appropriate read-out gain is set when the emitted light is being detected and converted into an electric signal to be used in the reproduction of a visible image on a recording material, such as photographic film, or on a display device, such as a CRT display device.
In the aforesaid image recording and reproducing systems which utilize X-ray film, stimulable phosphor sheets, or the like, and in various other systems which process general images, image read-out apparatuses are used in order to detect an image signal from a recording medium on which an image has been recorded (e.g. X-ray film or a stimulable phosphor sheet). In general, in the image read-out apparatuses, a recording medium, on which an image has been recorded, is scanned with a light beam. Light, which represents the image and is radiated out of the recording medium when it is scanned with the light beam, is detected and converted into an image signal by a photodetector. (For example, in cases where the recording medium is X-ray film, light which has passed through the X-ray film, or light which has been reflected by the X-ray film, is detected. In cases where the recording medium is a stimulable phosphor sheet, which is scanned with stimulating rays, the stimulable phosphor sheet emits light in proportion to the amount of energy stored thereon during its exposure to the radiation. The emitted light is detected.) In order for a visible image to be reproduced from the image signal, an image reproducing apparatus is used wherein intensity of a light beam is modulated in accordance with the image signal, and a recording medium, such as photographic film, is scanned with the modulated light beam.
In general, in order to scan a recording medium with a light beam in the aforesaid image read-out apparatus or the aforesaid image reproducing apparatus, a mechanical deflector, such as a rotating polygon mirror or a galvanometer mirror, is employed. However, mechanical movable parts of such a deflector generate vibration, which adversely affects the image read-out operations or the image reproducing operations. Also, the mechanical deflector cannot be kept small in size, and the service life of the mechanical movable parts is not long.